Hull of mechanically propelled vessels



Nov. 28. 1939. F. G'. PRATT v HULL 0Fl MECHANICALLY PROPELLED VESSELS Filed Nov. 26, 1937 Patented Nov. 28, 1939 UNITED STATES HULL OF MECHANICALLY PROPELLED VESSELS Francis Gordon Pratt, London,` England Application November 26, 1937, Serial No. 176,500 In Great Britain April 16, 1936 3 claims. (C1. 114-56) This vinvention relates to thehulls of mechanically propelled vessels.

It is well recognised that a large percentage of the resistance of ships and boats and more particularly vessels designed for high speeds, is due u to skin friction. With the object of reducing this friction, vessels having hulls furnished with transversely disposed steps in the under surface -have been proposed so that at high speeds the water will not be in contact with a section or sections of the underside, but the use of such vessels for practical purposes has been restricted by reason of the difficulties attached to producing a sufficiently strong construction and the inability to drive same at a high speed in rough water.

The object of the present invention is to improve the construction of hulls of abnormal form for high speeds by still further reducing the area of the under surface in contact with the water when travelling at high speeds, and to this end according to this invention it is proposed (a) to provide said vessels with two or more chines or bilges angularly disposed to one another in side elevation on each side of the keel or centre line and which remain immersed at the after ends at all times; (b) to arrange the sides and/or outer surfaces of the vessel above the chines slightly inboard of said chines, and ('c) to cut away a portion in the centre of the bottom of the hull for about one half or less of the length from the stern forwardly to form an inverted trench of any desired shape.

In the accompanying drawing: Figure 1 is a side elevation of a hull according to this invention; Figure 2 is an inverted half plan;

Figure 3 is a transverse midships section on line III-III of Figure 1;

Figures 4 to 8 are transverse half sections on the lines IV-IV to VIII-V111 respectively of Figure 1, and,

Figure 9 is an inverted plan of the aft end of a hull illustrating a modification.

Referring to the drawing, it will be vseen that the hull is provided with a centrally disposed surface I, the halves of which on either side of the keel or centre line are identical with or Without a physically defined junction, and on each side of said central surface with an outer surface ro 2 and a side member 3. The junctions of the central surface I with the outer surfaces 2, and of the outer surfaces 2 with the side members 3, are so formed as to produce sharp angles and the lower edges of the outer surfaces 2 and the 55 lower edges of the side members 3 are disposed slightly inboard in relation to the central surface I andfouter surfaces 2 respectively, said junctions constituting chines or bilges 4 and 5 on each side of the vessel.

It will further be seen that the central surface I is cut away from the point VI to the stern VIII to form an inverted trench 6.

It will be appreciated that in a vessel having a hull as herein described, the water displaced upwards and outwards from the under side of the surfaces I when the vessel is at speed will not follow the sharp angles 4 and 5 so that parts of the under and outer surfaces 2 and the side members 3 of the hull in contact with the water when the vessel is at rest will not remain in contact with the water when the vessel is at speed, thus reducing resistance dueto surface friction, and in like manner, that part of the central surface I forming the bottom of the inverted trench 6, will not be in contact with the water when the vessel is at speed, so further reducing resistance due to surface friction. It will also be seen that the water displaced by the central surface I when the vessel is at speed must come into contact with the outer portions of the after parts of the outer surfaces 2, thus being utilised to support the after end of the vessel and to reduce the surface friction on the outer surfaces 2 since the water displaced by the central surfacev I has forward motion already imparted to it whilst the spindrift of aerated water must further reduce the surface friction under the outer surfaces 2. In addition, it will be seen ,that the vessel remains water borne almost from the stem to the stern at all speeds and dynamic support due to motion is evenly distributed over the surfaces I and 2, in such a way as to ensure a maintenance of fore and aft and transverse stability at all speeds without any tendency to hunt or pivot longitudinally about any point, such as the main plane of a transversely stepped hydroplane or to ride on one longitudinal half or the other of the under surface as with an ordinary V-bottom formation of hull when driven at high speed, whilst the fine or sharp entrance or 45 bows will prevent the pounding or violent shocks to which other forms with bluff bows are subject.

In the modification illustrated in Figure 9, the hull has two chines or bilges 'I and 8 between the 50 keel or centre line and the outer chine or bilge f 9 on each side of the vessel, and the inverted trench 6 is arranged in stages, said trench extending for a part of its length transversely between the outermost of the inner chines 1 and 55 for the remainder of its length between the chines 3.

What I claim is:

1. A ships hull, relatively narrow with respect to its length, provided with a keel and a sharp water-cutting entrance, said hull comprising on each side of the keel, upper, intermediate and bottom portions angularly disposed in crosssectional view with regard to one another and meeting along longitudinal chine lines the chine lines between said upper and intermediate portions sweeping from the stern gradually upwardly towards the bow with respect to the normal load-waterline, said bottom portions widening from the bow rearwardly, and said intermediate portions being concave and inclined at a slight angle to the Vertical at the bow `and merging rearwardly with a screw twist into flat, substantially horizontal surfaces so gradually that the imaginary planes extending between the two chine lines bounding each of said intermediate 2. A ships hull, as claimed in claim 1, in which the bottom surface of the hull is provided with a step aft of amidships, the bottom surface portion rearwardly of said step lying above the adacent chine lines and sweeping rearwardly and upwardly .so as to form a centrally disposed inverted trench of rearwardly increasing depth, said trench being laterally closed throughout its length.

3. A shi-ps hull, as claimed in claim 1, in-

.cluding `ns extending longitudinally of the hull and projecting substantially horizontally from all the Achi-ne lines.

FRANCIS GORDON PRATI'. 

